We have previously demonstrated that mesenchymal stem cells (MSC), when injected into rodent hearts following myocardial infarction (MI), enhance myocardial repair and restore cardiac function. Moreover, this protective effect is enhanced by transduction of the MSC with the cytoprotective gene Akt (Akt-MSC). Furthermore, our data showed that these cells express paracrine mediators that reduce myocardial injury. In this application we hypothesize that Akt-MSC enhance myocardial repair, in part, through its paracrine effects on angiogenesis. Indeed we have shown in our laboratory that Akt-MSCs express multiple angiogenic cytokines such as VEGF and FGF. Moreover, media collected from these cells induce endothelial cell migration and tube formation in vitro. Importantly, we have recently demonstrated that Akt-MSC induces neovascularization in the infarcted heart. Since it has been shown that angiogenic signals mobilize bone marrow derived endothelial progenitor cells (EPC) that home to the ischemic myocardium, we hypothesize that (i) Akt-MSC increase angiogenesis in the post infarct heart through paracrine mechanisms and contribute to improved myocardial repair and function (ii) Akt-MSC increase angiogenesis in part through the recruitment of bone marrow derived EPCs and (iii) Akt-MSC mediated EPC recruitment is controlled by HIF 11. To test these hypotheses, we will investigate the capability of Akt-MSCs or media collected from these cells to stimulate EPC migration and tube formation in vitro and the ability to enhance neovascularization in the post infarcted heart in vivo. We will also examine the contribution of the potential Akt-MSC derived factors towards these processes. Next we will study the role of bone marrow progenitor cells in Akt-MSC induced neovascularization in ischemic myocardium in irradiated/bone marrow transplantation models using genetically marked donor cells. Moreover we will use a "suicide" gene delivery approache to selectively eliminate the bone marrow progenitor cells which may play a role in Akt-MSC mediated neovascularization. Finally, we will investigate the role of hypoxia and Akt regulated transcription factor HIF11 as a molecular switch which may regulate Akt-MSC induced bone marrow cell recruitment to the ischemic myocardium. These studies should help elucidate the mechanism by which Akt-MSCs provide such dramatic and long term protection of the infarcted myocardium and may identify potential therapeutic approaches. PUBLIC HEALTH RELEVANCE The protective effects of adult bone marrow stem cells in the injured heart have been demonstrated, however, the exact mechanism is unknown. In this study, we will examine the effects of these bone marrow cells in the development of new blood vessels in the infarcted heart. Enhancement of new vessels in the heart will greatly aid in the treatment of coronary vessel disease and heart failure.